imo it's the simplest counter other than the right hook, easier to land, more likely to keep the guy from throwqing the right hand so often. When I spar a southpaw my output goes way down if they counter me to the body like that.
Thanks for all the help guys, I'm still trying new methods to get around it but so far my most effective counter has been to feint a jab (to get him to throw the overhand right) then throw a right hook to the head. Last time I timed this perfectly and dropped him with it. Gotta make sure I keep my left up though to catch the overhand.
if your reflexes are fast enough you can take to steps to the right at da same time throwing to left straights.if im sparring someone who likes throwing the overhand right. Ill switch to southpaw temporally and ill hit them with that 2 punch combo. i like to land the 2 left straights right on there forehead.=)
Not read the rest of the suggestions, bit busy, but i would lean far back or even a little step back, and then get in your rear left uppercut as he's leaning forward and bent down a little bit.
if i'm getting this correctly he steps up with a big overhand right. have you tried hard pivoting around and drilling him with the straight left from the angle? if timing really is your thing you could hook him on the pivot(classic check hook) and then throw the left from the angle. i was never a big calzaghe fan when he was fighting but since he retired i've watched alot of his fights without the emotion and i've come to really admire the way he would pivot around on his front foot and totally open up the orthodox fighter